From WordNet (r) 3.0 (2006) [wn]:
needs
adv 1: in such a manner as could not be otherwise; "it is
necessarily so"; "we must needs by objective" [syn:
inevitably, necessarily, of necessity, needs]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Needs \Needs\, adv. [Orig. gen. of need, used as an adverb. Cf.
-wards.]
Of necessity; necessarily; indispensably; -- often with must,
and equivalent to of need.
[1913 Webster]
A man must needs love mauger his head. --Chaucer.
[1913 Webster]
And he must needs go through Samaria. --John iv. 4.
[1913 Webster]
He would needs know the cause of his repulse. --Sir J.
Davies.
[1913 Webster]